Chlorpyrifos (CPF) is a widely used pesticide which comes under the group organophosphorus (OP) [1]. They are commonly available in the form of white crystalline-like solids with slightly hydrophobic in nature and an affinity towards oily liquids [2]. In the year 1965 chlorpyrifos was brought into market to be used against insects, termites, mosquitos and beetles, particularly their larval stage [3, 4]. Chlorpyrifos kill the pest by malfunctioning their nervous system. When the pest is infested with chlorpyrifos, they block the enzyme acetylcholinesterase which results in the accumulation of acetylcholine in the synapse. This leads to overstimulation of neuronal cells and muscle spasms which eventually causes the death of pests [5, 6].
In the present scenario, agriculture practices to increase the crop yield pesticides are still used even though they have some drawbacks if not used properly. The pesticide CPF is mainly used to control soil pests, foliar treatments and directly applied in cattle, sheep etc to control fever ticks, ear ticks, lice and so on [7–9]. For soil treatment, concentrations ranging from 300 to 4000 g/ha are applied in the forms of emulsions, granules etc. After the application of CPF 20 to 60 days of withdrawal period is needed prior to harvest [10]. The prolonged usage of these pesticides can lead to deposition of its residue in the environment. However, if the residue content is below the MRL (maximum residue limit) it is safe to use [11]. The higher dose of lipophilic Chlorpyrifos (CPF) on agriculture crops may increase the chances of bioaccumulation of pesticide, the leftover residue will remain on vegetables, crops and fruits hence entering into the food/feed chain through the consumption of crop-by products by livestock. Higher doses of CPF exposure can cause several health hazards in humans as well as in animals. Intake of crops and vegetables containing higher amounts of CPF residue can cause metabolic abnormalities, chronic neurotoxicity, gastrointestinal effects, musculoskeletal effects etc. Eventually, over usage of these pesticides can also lead to the damage of aquatic and terrestrial ecosystems. Some of the American and European countries have already restricted the domestic usage of CPF due to the human health risk [12–15]. Thus, proper evaluation and monitoring of these pesticide residues in the natural vegetation and crops is inevitable.
Various methods are available for isolation and detection of CFP such as enzyme inhibition methods [16], immunization assays [17], flow cytometry [18] and chromatography. Among the available methods, chromatographic methods are the widely used one. Commonly used chromatographic methods include, Thin Layer Chromatography (TLC), Liquid Chromatography (LC), High Performance Thin Layer Chromatography (HPTLC) and Gas Chromatography (GC). Coupled with specific chromatography, various detectors such as mass spectrometry, Flame ionization detector, Electron capture detector, Near-Infrared spectroscopy etc. are used [19].
Extraction and clean up methods prior to the analysis is an important step. There are many conventional methods available such as Soxhlet extraction, sonication extraction, homogenization with solvents etc. However, these traditional methods have many drawbacks like wastage of solvents, time consuming procedures and so on. Many advanced techniques are available today in order to overcome such drawbacks. Among the advanced methods, solid phase extraction (SPE), solid phase microextraction (SPME) and the quick, easy, cheap, effective, rugged and safe (QuEChERS) dispersive solid phase extraction are the widely used effective methods [20]. For pesticide residue analysis QuEChERS method is the most effective method. This method is developed by Anastassides and his team which have many advantages like its simplicity to use, minimal solvent use, good extract recovery and can be used for wide ranges of pesticides [21]
In this study we have used QuEChERS extraction methods and Gas chromatography coupled with a micro electron capture detector to estimate the presence of chlorpyrifos pesticides in the feed samples. Electron capture detector with gas chromatography (GC-ECD) is a suitable method for determining low concentrations in the range of parts per billion. Since chlorinated organic pesticides contain high electron affinity, detection and measurement of CPF with GC-ECD was more accurate [22].